Such devices are intended to connect in a flexible manner, pipes that are subject to vibration, and to protect them from vibration. In order to meet the requirements of the automotive industry (passenger cars) for gas-tightness, a metal bellows-type is often part of such decoupling elements. As the large diameter variations in the convolutions of the metal bellows may lead to turbulences, a metal hose is usually incorporated into the pipe so as to ensure laminar gas flow. It must be ensured that noise generated during operation resulting from the metal hose hitting the inside of the bellows is kept to a minimum. This is often achieved by surrounding the hose with a braiding. DE 198 20 863 A 1 shows a flexible pipe as an example. Instead of using braiding, the metal hose and the metal bellows are connected at defined points so as to prevent the noise development described above.
In the range of commercial vehicles, multi-layer, stripwound metal hoses produced from profiled strip material are frequently used as decoupling element in exhaust systems. Since residual leakage is low yet permissible, it is not necessary to use a gas-tight element such as a metal bellows. A simple example of metal hoses used as decoupling elements is the so-called Agraff hose. Further examples, which exhibit a longer service life and a lower leakage rate than Agraff hoses, have been described in publications DE 344 1064 C2 and U.S. Pat. No. 6,488,052 B2.
Stripwound metal hoses are especially suitable for the exhaust systems of commercial vehicles as they allow for large offsets in the axial, lateral, and above all the torsional direction without structural tension being generated. Their disadvantage, however, is the remaining leakage.
As legal provisions worldwide will be stipulating a clearly reduced emission of pollutants from commercial vehicles, exhaust systems will increasingly be fitted with post-treatment modules such as soot filters and SCR systems. Leakage that may allow untreated exhaust gas to emerge from the system will be permissible only to a limited extent.